The invention relates to a cathode ray tube comprising an envelope having a conical portion, a high-voltage contact, a resilient strip having a longitudinal direction and first and second end portions which are detachably secured to the high-voltage contact inside the envelope, the first end portion comprising a getter cup, said envelope having at least one protrusion on its internal side.
A cathode ray tube having a protrusion on the internal side of its envelope is disclosed in DE-U 7726914. The cathode ray tube according to the prior art comprises a high-voltage contact to which a resilient strip is detachably secured. A cup, which contains a getter material, is mounted at one end of the resilient strip. In a certain phase of the manufacturing process of the cathode ray tube, the resilient strip is secured to the anode contact. At a later stage, the getter material is heated, which causes the getter material to evaporate. Finally, after cooling, the tube is internally covered with a thin layer of getter material ensuring that proper vacuum conditions are maintained within the tube.
The resilient strip is detachably secured to the anode contact and may rotate freely around the high-voltage contact. If no precautions are taken, there will be a risk that the resilient strip might become rotated with respect to its initial position during further processing. Then, the dispositioned resilient strip with the getter cup might cause a getter layer at the wrong location within the tube or might result in non-uniformity of the deposited getter layer. Consequently, the vacuum conditions within the tube may not meet the quality requirements, which will lead to scrap. In order to prevent dispositioning, the envelope of the cathode ray tube according to the prior art internally comprises a protrusion near the getter cup. A resilient metal w-shaped element, which engages the protrusion, is mounted on the getter cap. The getter engagement according to the prior art has the disadvantage that the specific location of the protrusion near the getter cup may affect the quality and uniformity of the layer.